Diluent recovery process

ABSTRACT

An improved process for separating a volatile organic diluent from a low density olefin polymer in solution of suspension comprises vaporizing the diluent with steam and water at an elevated temperature and separating a slurry of polymer and water; discharging a vapor stream containing a small amount of polymer particles into a cyclone vessel; withdrawing the vapors substantially free of polymer and recovering the diluent; and removing the separated particles from the cyclone with a flow of water at a downward velocity exceeding the rise velocity of the particles through the water to prevent agglomeration of the particles.

United States Patent Lauck [54] DILUENT RECOVERY PROCESS [72] Inventor:John D. Lauck, lll Crestwood Drive, Parkersburg, W. Va. 26101 [22]Filed: Nov. 5, 1970 [21] Appl. No.: 87,046

[52] US. Cl ..260/85.1, 260/88.2 B, 260l93.l, 260/93.5 S, 260/93.5 A,260/93.7, 260/94.7 R, 260/94.9 F, 260/878 R, 260/880, 260/886 [15]3,684,783 51 Aug. 15,1972

Primary Examiner-Joseph L. Scholer Assistant Examiner-A. HollerAttorney-Martin S. Baer and William H. Myers ABSTRACT An improvedprocess for separating a volatile organic diluent from a low densityolefin polymer in solution of suspension comprises vaporizing thediluent with steam and water at an elevated temperature and [51] Int ClCost Cosd 5/00 separating a slurry of polymer and water; discharging[58] Field "260/94 9 93 7 85 l a vapor stream containing a small amountof polymer particles into a cyclone vessel; withdrawing the vaporssubstantially free of polymer and recovering the [56] References Citeddiluent; and removing the separated particles from the UNITED STATESPATENTS cyclone with a flow of water at a downward velocity exceedingthe rise velocity of the particles through the 32:2 3 a1 water toprevent agglomeration of the particles. 3:296:240 l/1967 MacDonald etal...260/94.9 E 4 Claims, 1 Drawing Figure 2| T0 SOLVENT 32 i RECOVERY It l 1; WATER --mxms zone a I STEAM i \\CYCLONE 'VESSEL/ '2 I YISEPARATION ZONE l POLYMER A 42 43 44 a DILUENT Io 45 3e CONTACTORPRODUCT- WATER DEWATERING DILUENT RECOVERY PROCESS This inventionrelates to a method for separating a volatile organic diluent from anolefin polymer in solution or suspension. More particularly it relatesto removal of finely divided solid polymer from vapors resulting fromheating the mixture of polymer and diluent with steam and water at anelevated temperature.

A wide variety of processes are knownin the art for the preparation ofsolid polymers of olef'ms. Often such polymerization processes employvolatile organic liquids as diluents or reaction media. In some of theseprocesses the polymer is produced in the form of a solution or as aslurry in diluent, and must be recovered therefrom. Separation of thediluent can be successfully accomplished in a process comprisingcontacting a mixture of polymer and diluent with steam at an elevatedtemperature, e.g., in an apparatus such as described in U.S. Pat. No.3,050,] 13 to Rundquist. In

said apparatus the mixture of polymer and diluent enters one conduit,steam under pressure enters a second conduit, and a mixture of steam,polymer and diluent is sprayed through a nozzle outlet into a vesselcontaining water from which the solvent vapor is withdrawn and is cooledand processed for re-use.

A difficulty arises that the polymer often has a density less thanwater, causing it to rise to the surface. This,

and the turbulence of vaporization, sometimes results in a considerableamount of particulate polymer being entrained in the mixed vapors ofsolvent and water. These polymer particles adhere and accumulate on thesurfaces of heat exchanger equipment used to cool the vapor stream. Theaccumulated polymer generally has low heat transfer properties, therebyreducing the efficiency of the heat exchange equipment. In a like mannerthe polymer particles, particularly rubber polymers, tend to agglomerateand adhere to conventional particle separation means such as cyclones,screens, filters, and the like, reducing their efficiency and requiringfrequent cleaning. Such cleaning is often disruptive of continuousoperation of the process. It is thus an object to provide a method forremoving particulate olefin polymer contained in a vapor stream. Anotherobject is to provide a method for minimizing equipment fouling bypolymer. A further object is to provide a method for separating avolatile diluent from a polymer having a density less than water. Astill further object is to provide a method for recovering the polymerfrom the diluent vapor in a continuous manner. Yet another object is toprovide an improved method for separating rubbery olefin polymers from aslurry or solution of said polymers in a volatile organic liquid.

The above and other objects of the invention will be understood by thoseskilled in the art from the following specification and claims.

According to the invention, a method is provided for separating a solidpolymer of a least one olefin from a mixture of said polymer with avolatile organic diluent which comprises contacting said mixture withsteam to form a contact product; mixing said contact product in a mixingzone with water at an elevated temperature to form a slurry of polymerand water; withdrawing said slurry from said mixing zone; passing fromsaid mixing zone mixed vapors of solvent and water and containingparticulate solid polymer into an upright centrifugal vapor-solidseparation zone, e.g., a cyclone vessel whose upper dimension isselected to optimize deentrainment of the particles; passing from theseparation zone a vapor stream substantially free of polymer;introducing water into the upper section of said separation zonesufficient to maintain liquid phase on the upright surfaces and tomaintain a level of liquid comprising an aqueous slurry of polymer atthe lower exit of the separation zone; withdrawing from said lower exitof the separation zone said aqueous slurry at a rate wherein thedownward velocity of the water exceeds the rise velocity of the solidpolymer through the water. The aqueous slurry from the cyclone may bediscarded, but advantageously is treated to recover the polymer. Thevapor stream substantially free of polymer is subsequently cooled andthe diluent recovered for re-use.

By using the method according to the invention, the particulate solidpolymer being removed from the cyclone is substantially prevented fromagglomerating and fouling or plugging the cyclone and downstream processequipment. An additional feature is that the slurry recovered from thecyclone may be recycled to the mixing zone for recovery together withthe principal polymer, by conventional water separation techniques. Thepresent invention can be carried out in an apparatus as shown in theaccompanying diagrammatic illustration. A mixture of an olefin polymerand volatile organic diluent, e.g., from a polymerization reactor (notshown), such as a mixture of lillpercent by weight polybutadiene in ahydrocarbon diluent boil ing between and 1601 F is charged via conduit10 to contractor l4 and contacted with steam l2 and is passed viaconduit 16 to a mixing vessel 18 containing hot water. The mixing vessel18 is equipped with mixing means 20, e.g., a propeller agitator drivenby motor means 21 to keep the polybutadiene suspended as a slurry in thehot water. The aqueous slurry of polymer is withdrawn via conduit 22 toconventional liquidsolids separation means 24, such as centrifugation,filtration, screening and the like. The polybutadiene removed viaconduit 23 may be further dried by conventional means (not shown), suchas a hot air dryer. The separated water removed via conduit 26 may bediscarded or re-used. The mixing in vessel 18 is ordinarily carried outat elevated temperatures, e.g., 1505490 1 and at more preferably in therange between .and 260 .E and pressures in the range between :10 and f50psig, preferably, however, at an elevated pressure, e.g., autogenouspressure in the range between about 3-50 psig, more preferably betweenabout 5 and 40 psig; the particular tempera ture and pressure may varyaccording to the volatility of the particular organic diluent. Water maybe added to the mixing zone via conduit 30. Heating of the mixing zonemay be accomplished by any conventional method, e.g., via steam enteringwith the contact mixture, by heating the mixing vessel (not shown), orby heating the water added via conduit 30 by auxiliary heaters (notshown). Vapors from the mixing vessel are passed as a mixture of diluentand water vapor containing a small amount of entrained solid polymer viaconduit 32 disposed from the upper portion of the mixing vessel to aseparation zone here shown as cyclone vessel 34 wherein the solidpolymer is removed, and the mixed solvent and water vapor is passed viaconduit 33 from the upper exit of the cyclone. The substantiallypolymer-free mixed vapors are passed to chilling equipment (not shown)for condensation, and the diluent thereafter separated from the water byconventional techniques such as decantation, centrifugation,fractionation and the like, and recovered for re-use.

In the upper part of cyclone 34, water is provided via conduit 35 toflow on the upright surfaces and carry the particles of solid polymer toa lower exit 36 where a water seal is maintained to avoid loss ofsolvent vapor. The seal may be maintained by level controlling means(not shown). The flow is adjusted such that the downward velocity of thewater at the exit end exceeds the rise velocity of the solid polymerthrough the water, whereby the particles are prevented from floating tothe upper surface of the water seal and agglomerating. Downward watervelocities are suitable in the range from about 1.2 to about 8feet/second. The mixture of polymer and water is removed from the lowerexit end of the cyclone via conduit 37 and is passed by any conventionalmethod, e.g., by pump means 38, via conduits 40 and 42 to mixing zone18.In a preferred embodiment a substantial portion of the discharge ofpump means 38 is recycled via conduits 40, 43, valve 44, and conduit 45to the lower portion of cyclone 34, whereby the amount of waterintroduced to cyclone 34 via conduit 35 can be maintained at an economiclow level.

The process according to the invention may suitably be employed withpolymers of olefins having up to about nine carbon atoms, e.g.,ethylene, propylene, cyclopentene, butadiene, isoprene, styrene,alphamethyl styrene and the like. The polymers may be homopolymers, orgraft, random or block copolymers of said olefins. The process issuitable for olefin polymers having a density less than water, e.g., aspecific gravity in the range from about 0.80 to about 0.98, and morepreferably between about 0.90-0.97. Moreover, the process findsparticular utility with rubbery, i.e., predominately non-crystallinepolymers such as, e.g., styrene butadiene copolymers wherein the problemof agglomeration of particles under diluent recovery conditions is mostsevere. In accordance with the ASTM definition, a rubbery polymer hereinrefers to a material which at room temperature can be stretchedrepeatedly to at least twice its original length and upon immediaterelease of the stress will return with force to its approximate originallength.

These polymers are produced by a wide variety of processes employing,e.g., organometallic catalysts of the so-called Ziegler-Natta typewherein a compound of a transition metal of Group IV to VIII such ascobalt chloride is reduced by a strong reducing agent such as anorganometallic compound of a Group I to III metal such as, e.g.,aluminum triethyl. Other known processes employ, e.g., any of a varietyof hydrocarbyl lithium catalysts.

Many of these processes employ as diluent volatile organic liquids,e.g., hydrocarbons of about four to 10 carbon atoms such as butane,n-pentane, isopentane, cyclohexane, heptane, petroleum ether, benzene,toluene and the like. Exemplary processes are described for example inU.S. Pat. No. 3,066,127 to Carlson et al., U.S. Pat. No. 3,265,765 toHolden et al, and U.S. Pat. No. 3,480,696 to Hassell et al. In addition,the process according to the invention applies as well to separation ofmixtures of polymer and diluent employed, e.g., in processes forhydrogenation of the polymer, solvent blending, and the like.

The process of the invention may be better understood by reference tothe following description of a specific embodiment as applied to theaccompanying drawing. A mixture of 10 percent by weight of polyisoprenein isopentane is charged to the contactor and contacted with steam atabout psig, the product passed to the mixing vessel 18 containing waterat 190 F. The pressure in mixing vessel 18 is about 20 psig. Polymer andwater is withdrawn from the mixing zone. Mixed vapors of steam andisopentane in a weight ratio of about 1.221 and containing a smallamount of polyisoprene particles are passed at relatively high velocityvia conduit 32 to cyclone 34 and the mixed vapors substantially free ofpolymer are passed via conduit 33 to be cooled and diluent recoveredtherefrom. The walls of the cyclone are rinsed by tangential flow ofwater at a rate of about 1 gallon per unit of time. A dilute slurry ofdeentrained polymer in water is removed from the exit end of the cycloneat a linear velocity of about 3 feet/second whereby the polymerparticles are prevented from floating to the surface and forming a mat.The flow rate of the dilute aqueous slurry is about 4 gallons per unitof time, via conduit 37, pump 38 and conduit 40. The flow of aqueousslurry is divided and regulated such that 3 gallons per unit of timeflows via conduits 40, 43, valve 45 and conduit 44 to recycle to thelower portion of cyclone 34; the remainder of the dilute aqueous slurryis passed from pump 38 via conduits 40 and 42 to the mixing zone 18.

I claim as my invention:

1. In a process for separating a solid rubbery polymer of a monomericolefin of up to nine carbon atoms from a mixture of said polymer with avolatile organic diluent which comprises contacting said mixture withsteam to form a contact product, mixing said contact product with waterin a mixing zone at an elevated temperature in the range between and 260F to form a slurry of polymer and water and a vaporous mixture ofdiluent and steam; withdrawing said slurry from said mixing zone;passing from said mixing zone the vaporous mixture of solvent and waterand containing entrained particulate solid polymer into an uprightcentrifugal vapor-solid separation zone; withdrawing from saidseparation zone a vapor stream substantially free of polymer;introducing water into the upper section of said separation zone,sufficient to maintain liquid phase on the interior upright surfaces andto maintain a liquid seal comprising an aqueous slurry of polymer at thelower exit end of said separating zone; the improvement comprisingwithdrawing from said separating zone said aqueous slurry at a ratewherein the downward velocity of the water in the liquid seal exceedsthe rise velocity of said polymer through the water.

2. A process as in claim 1 wherein said olefin polymer has a specificgravity in the range from about 0.80 to about 0.98.

3. A process as in claim 1 wherein at least a portion of the aqueousslurry from said separation zone is recycled to the lower portion ofsaid separating zone.

4. A process as in claim 1 wherein said volatile organic diluent is ahydrocarbon of about four to 10 carbon atoms.

UNITED STATES PATENT OFFICE 7 CERTIFICATE OF CORRECTION Patent No. 1 M75 Dated'A 15, 197

Inventor(s) JOHN D. LAUCK It is certified that error appears in theabove-identified patent and that said Letters Patentare hereby correctedas shown below:

r: Follcming the inventor's name end address in the heading of thepatent, reference to the assignment has been I omitted, which referenceshould read: I

"assignor to Shell Oil Company, New York; N oYo Signed and sealed this15th day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

2. A process as in claim 1 wherein said olefin polymer has a specificgravity in the range from about 0.80 to about 0.98.
 3. A process as inclaim 1 wherein at least a portion of the aqueous slurry from saidseparation zone is recycled to the lower portion of said separatingzone.
 4. A process as in claim 1 wherein said volatile organic diluentis a hydrocarbon of about four to 10 carbon atoms.